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New Framework for Understanding Cross-Brain Coherence in Functional Near-Infrared Spectroscopy (fNIRS) Hyperscanning Studies

Published: October 6th, 2023



1The Department of Behavioral Sciences and Psychology, Ariel University, 2Braude College of Engineering, 3Department of Psychology and Behavioral Sciences, Zhejiang University, 4Department of Psychology, Florida Atlantic University

Wavelet transform coherence (WTC) is a common methodology for assessing the coupling between signals that is used in functional near-infrared spectroscopy (fNIRS) hyperscanning studies. A toolbox for assessing the directionality of the signal interaction is presented in this work.

Despite the growing body of functional near-infrared spectroscopy (fNIRS) hyperscanning studies, the assessment of coupling between two neural signals using wavelet transform coherence (WTC) seems to ignore the directionality of the interaction. The field is currently lacking a framework that allows researchers to determine whether a high coherence value obtained using a WTC function reflects in-phase synchronization (i.e., neural activation is seen in both members of the dyad at the same time), lagged synchronization (i.e., neural activation is seen in one member of the dyad prior to the other member), or anti-phase synchronization (i.e., neural activation is increased in one member of the dyad and decreased in the other). To address this need, a complementary and more sensitive approach for analyzing the phase coherence of two neural signals is proposed in this work. The toolbox allows investigators to estimate the coupling directionality by classifying the phase angle values obtained using traditional WTC into in-phase synchronization, lagged synchronization, and anti-phase synchronization. The toolbox also allows researchers to assess how the dynamics of interactions develop and change throughout the task. Using this novel WTC approach and the toolbox will advance our understanding of complex social interactions through their uses in fNIRS hyperscanning studies.

In recent years, there has been a shift in the types of studies conducted to understand the neural bases of social behavior1,2. Traditionally, studies in social neuroscience have focused on neural activation in one isolated brain during a socially relevant task. However, advances in neuroimaging technology now allow for the examination of neural activation in the brains of one or more individuals during social interaction as it occurs in "real-life" settings3. In "real-life" settings, individuals are able to move freely, and patterns of brain activation are likely to cha....

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The study was conducted at Florida Atlantic University (FAU) and was approved by the FAU Institutional Review Board (IRB).

1. Using Homer3 software (Table of Materials) to perform the pre-processing of the fNIRS hyperscanning data

NOTE: Homer3 is a MATLAB application that analyzes fNIRS data to obtain estimates and maps of brain activation29. Homer3 can be downloaded and installed from the following link (

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This section demonstrates the types of analyses that can be carried out with the toolbox (which can be downloaded at or For these analyses, fNIRS data collected with a small sample of infant-parent dyads were utilized. Six pairs of mother-infant dyads were tested using a validated behavioral task, the free-play task31, which is as close to a real-life infant-mother interaction as possible. Prior to .......

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One of the most common methods used in fNIRS studies is wavelet transform coherence (WTC), which is a measure of the cross-correlation of two time series as a function of frequency and time10. WTC calculates the coherence and phase lag between two time series using correlational analyses (Supplementary File 1). FNIRS hyperscanning studies have used WTC to estimate IBS in many domains of functioning, including action monitoring12, cooperative and competitive.......

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We would like to acknowledge the support provided by the National Natural Science Foundation of China (No. 62207025), the Humanities and Social Sciences Research Project from the Ministry of Education of China (No. 22YJC190017), and the Fundamental Research Funds for the Central Universities to Yafeng Pan.


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Name Company Catalog Number Comments
NIRScout   NIRx Medical Technologies, LLC n.a. 8 sources, 8 detectors
MATLAB The Mathworks, Inc. Matlab 2022a In this protocol, several toolboxes and buit in MATLAB functions were used: HOMER3 toolbox was used to convert Intensity to OD, to remove motion artifacts through its function hmrMotionCorrectWavelet with default parameters and to convert OD to Conc. Wavelet Toolbox was used to compute WTC.

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